CATARACT EWAP SEPTEMBER 2023 13 IOL with negative spherical aberration or neutral spherical is theoretically preferred, Dr. Fram said. Conversely, a patient with a hyperopic ablation, which Dr. Fram said is more challenging to obtain consistent keratometry measurements with, can cause negative or neutral spherical aberration. This, with a small pupil, can lead to a multifocal-like outcome. If the patient was previously happy with this ablation pattern without cataracts, Dr. Fram said she’ll often choose IOLs with zero spherical aberration. “The question often arises whether to choose an EDOF or diffractive multifocal/ trifocal technology in the post-corneal refractive population,” Dr. Fram continued. “There are many reports of excellent outcomes with this technology. In our experience, the ablation needs to be well centered with normal Placido imaging in order to have a satisfied patient. Some refer to the EDOF technology as ‘more forgiving’ than a multifocal or diffractive technology. However, if a surgeon is going to use this technology, they need to be prepared to remove the IOL because up to 19% of post- LASIK patients had to have an IOL exchange due to diffractive dysphotopsia, according to our research.” 1 This is where Dr. Fram finds the Light Adjustable Lens (LAL, RxSight) beneficial. “The LAL has been a huge boost for our practice in the post-LASIK/PRK patient population [because] the IOL targeting can be adjusted postoperatively and is less reliant on current IOL calculations,” she said. “This has become my preferred technique due to the postoperative adjustability, and the silicone IOL lends itself to a lower dysphotopsia profile in these already aberrated corneas.” While it’s still necessary with the LAL for the patient to have a well-centered ablation, normal Placido imaging, and a pupil that can dilate to at least 6.5 mm, Dr. Fram said the technology can achieve a customized mini - monovision without the need to disassociate the eyes more than 1.5 D. “Patients need to understand this is still a monovision strategy and they will need glasses for some tasks depending on the amount of anisometropia, such as driving at night and reading very small print. When we looked at the number of post-myopic LASIK ablation patients (n=35) achieving stable ±0.5 D at 1 year, it was 87%. Although this is a very small study group, the results are promising. Further, this has not been reported consistently in the literature in the post-laser vision correction population.” For Dr. Hill, the most important part of IOL selection with patients who have had prior refractive surgery is their aberration profile. “Those patients with significantly elevated higher order aberrations, such as coma and spherical aberration, are generally not multifocal IOL candidates,” Dr. Hill said. “This is reinforced by the image simulation, which typically demonstrates a loss of contrast.” IOL calculations Dr. Hill said the “go-to” IOL formula for those with prior refractive surgery is the Barrett True-K. If the patient is a toric candidate, and he said that this is uncommon, he’ll use the Barrett True-K Toric with the measured posterior corneal power. “For those patients who absolutely have to have an exact refractive outcome, the LAL is used,” he said. Dr. Fram said that many patients with prior refractive surgery expect to have similar refractive results after cataract surgery. However, their modified anterior corneal curvature isn’t accurate with traditional formulae that are based on assumptive keratometry principles. Dr. Fram cited research that has shown previous formulas developed for post-laser vision correction eyes, relying on historical keratometry, were within ±0.50 D of target less than 60% of the time. These, she noted, were eliminated from the ASCRS calculator. When post-laser vision correction ablation data are available, the Masket Regression formula achieves 85% within ±0.5 D and 95% ±1 D of target. 2 Newer formulae that don’t require historical data and intraoperative tools have further improved outcomes for these patients, Dr. Fram said. “Abulafia et al. reviewed the Barret True-K formula outcomes and found the Barrett True-K was comparable to results of the ASCRS calculator with a median absolute error of 0.33 Editors’ note: Dr. Fram practices at Advanced Vision Care, Los Angeles, California. Dr. Kim is in private practice with Professional Eye Associates, Dalton, Georgia. Neither disclosed relevant financial interests. What’s one thing you think surgeons should be doing with post-refractive patients who are cataract surgery candidates that many aren’t doing already? Dr. Fram: Understand the advancements in formulae, try to not leave the consenting process to a surgical counselor alone, and be prepared for an IOL exchange (particularly if using diffractive technology and/or if you do not have access to the LAL). Dr. Hill: Take all the time necessary to explain the limitations involved in the process. Essential items are: 1) This is not routine surgery for which all options are possible; 2) the calculation accuracy is less than for regular cataract surgery; and 3) the reduced contrast from elevated higher order aberrations will persist, especially at larger pupil sizes. Use image simulation to demonstrate what the postoperative vision will be. continued on page 15
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